The phase diagram of the ternary system potassium laurate-1-decanol-D${}_2{}^{}{}_{}{}^{}\mathrm{O}$ was studied over concentration ranges where nematic phases are likely to occur. Two uniaxial nematic phases which are separated by a biaxial nematic phase are found. In limited concentration range the following phase sequence may be observed reversibly on heating and on cooling: isotropic-uniaxial nematic (positive optical anisotropy)-biaxial nematic-uniaxial nematic (negative optical anisotropy)-biaxial nematic-uniaxial nematic (positive optical anisotropy)-isotropic.

• Received 9 June 1980

DOI:https://doi.org/10.1103/PhysRevLett.45.1000